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For the purpose of comparative histology and histomorphometry of the ovaries and ovarian follicles of local (West Azarbayjan of Iran) and leghorn chickens (layer strain) from each group five pullets (4-5 months old), five adult layers (6-18 months old), and five old layers (more than 19 months old) were selected i, e 30 birds (15 local, and 15 leghorns). There were highly significant differences (p < 0.00 1) in mean weight of ovaries between old local and leghorn hens, where as between local pullets, and leghorn pullets as well as local layers and leghorn layers there was no significant differences. There was no significant differences in mean distribution of healthy follicles between local and leghorn pullets, but this was highly significant (P < 0.001) between local and leghorn layers and significant (P < 0.05) in local and leghorn old hens. The differences of mean distribution of atretic follicles in local and leghorn pullets was not signigicatn. where as this parameter showed highly significant (P < 0.00 1) differnces in local and leghorn layers as well as in local and leghorn old hens. The comparative study of the
mean distribution of the healthy follicles with the different sizes between local and leghorn pullets showed no significant differences in any of sizes under study, where as in two groups of healthy follicular sizes i. e < 100 1um and 101 -400 m , there was significant (P < 0.00 1) differences between local and leghorn layers. Conversely , in these group. the mean distribution of healthy follicles with sizes of 401 - 400um and above That
showed no significant differences. In comparative study of mean distribution of atretic follicles with < 100 m in local and leghorn pullets, there was no significant differences, where as mean distribution of atretic follicles with sizes of 101 - 400,um and 401 - 4000 m and above that, there were highly significant (P< 0.00 1), differences and incidences of follicular atresia in local pullets were higher than to that of leghorn pullets. the comparative study of follicular atresia in local and leghorn layer hens revealed that on all of the three sizes (100 um,101 - 400am, 4001- 4000 urn, and above) differences was highly significant. Therefore in these groups, follicular atresia was very higher in local layers than the leghorn layers. This was true in the case of old local and old leghorn hens too. We conclude that, follicular atresia in all the three groups (pullets, layers, and old hens) is higher in local chickens than the leghorn chickens, and this condition may be one of the very inportant factors for low egg production in local chickens of under study.